Control: found -1 7.1um1 (By the way, why don't we make the version number for the user-mode-linux binary package reflect the version of linux-source-* package that was used at build-time, so that rebuilds of user-mode-linux against newer linux-source-* packages will be identified as upgrades? The version numbers of binary packages need not have any relation to their source packages. The status quo is also troublesome for bug reports like this, because '7.1um1' isn't a useful identifier for the kernel used. If there's not a particular reason for this I can try a merge request.)
I ran into this issue in a quite different context, having built user-mode-linux against 7.1.8-1~bpo13+1 on Trixie and wanting to give it a try to investigate a kernel issue. A succinct statement and a patch were proposed in 2024 at https://lore.kernel.org/all/[email protected]/ but it doesn't seem like anything happened to it and it was just forgotten. Here's a clear manifestation: /usr/share/doc/user-mode-linux/README.Debian includes the conventional advice of > Kernel modules > -------------- > Modules are installed in /usr/lib/uml/modules/<version>. The easiest way to > get to them from within UML is to use hostfs, e.g.: > mount -t hostfs -o /usr/lib/uml/modules hostfs /lib/modules > or: > echo "hostfs /lib/modules hostfs /usr/lib/uml/modules 0 0" >> /etc/fstab Note that the subdirectory of the host is specified as a "keyless" mount option, and the source device name (the word "hostfs" here) is not used but ignored. This doesn't actually work anymore though: > ~# mount -t hostfs -o /usr/lib/uml/modules hostfs /lib/modules > mount: /usr/lib/modules: fsconfig() failed: hostfs: Unknown parameter > '/usr/lib/uml/modules'. > dmesg(1) may have more information after failed mount system call. It's buried very deep in the mailing list thread at https://lore.kernel.org/linux-um/[email protected]/ but I found that using a key name of "hostfs" makes everything work: > ~# mount -t hostfs -o hostfs=/usr/lib/uml/modules hostfs /lib/modules > ~# ls /lib/modules > 7.1.8 (correct!) So if this apparent regression is not going to be fixed in the kernel, being a couple years old at this point, we need to update documentation to use the "hostfs=" key. We ought to do this in README.Debian, but also no other documentation about UML (Rob Landley's site, kernel.org UML HowTo v2, ...) has addressed this yet. This is why it's been so hard for me to find.
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